Mesa Merge Pending For Vulkan Ray-Tracing On Older AMD GPUs

Merged yesterday for Mesa 21.3 was open-source Vulkan ray-tracing for AMD RDNA2 / RX 6000 series GPUs with the RADV driver. Opened today now is a merge request that would provide Vulkan ray-tracing with RADV to pre-RDNA2 GPUs on this driver going back to the likes of Polaris, granted the performance is another story.

Joshua Ashton known for his work on DXVK and other Direct3D-on-Vulkan efforts for Valve has opened the merge request to enable RADV Vulkan ray-tracing for older generations of AMD GPUs.

Ashton noted with the MR, "This PR implements ray-tracing for older generations (Navi, Vega, Polaris, etc.) It does this by emulating the AMD bvh intersection instructions in software. Right now this passes CTS the same as on RDNA 2 cards."

So it's working on older GPUs, has the same conformance test suite (CTS) passing rate as the proper RDNA2 support, and is relying on software/shader-based support and thus the performance will likely suffer as a result. As it stands right now even for the RDNA2 ray-tracing on RADV the performance is far from in good shape and will need some optimizations before it's comparable to the proprietary driver.

Ashton had been experimenting for several months with this RADV ray-tracing for older GPUs. AMD has not supported any Vulkan (or DirectX DXR) ray-tracing with their pre-RDNA2 GPUs in their official drivers. AMD also hasn't provided any official open-source driver support at all around Vulkan ray-tracing in their AMDVLK reference driver.

The merge request is just 300 lines of new code for this software-based ray-tracing support. Besides landing this code, the RADV_PERFTEST=rt environment variable is also needed. This MR will hopefully land in time for Mesa 21.3 barring any objections from being raised.